The only way entropy can be reversed in a system is if the system is open and not isolated. So, where are these isolated systems that manage to have a decrease in entropy? Just one example is all I need.
Well, Entropy is the more general term (i presented a very common, and more clear for everyone example tied to most calculations of thermal-based changes in a system, eg when an icecube melts in a glass of water, using also the difference in temperature between the room and the water and ice-cube). Entropy itself, ultimately, is the main term in thermodynamics and related systems (i have been reading some Caratheodory on this too
). But Entropy is (afaik this definition is accurate and workable) the degree of diminishment of ability in a system to change. So, according to some phrasings of the second law of Thermodynamics it is argued that the entropy of any system (eg the 'universe', if that can/could be deemed as an isolated system) always increases, and so tends to a maximum.
If the entropy becomes the maximum, then (by definition) the system can no longer have any changes (or "works", to use the physics term).
But those above presuppose a number of things:
1) That we have an actual isolated system as the 'universe'
2) That any phenomena which would instead alter the flow of entropy, are not there at all cause they are not examined by now
Which is why i noted that if we come to include other parameters (don't know which, obviously, if they are examined), then we may find that there is not an adiabatic (ie one-direction) alteration/progression of entropy in a system. Maybe there are more directions, or maybe the system itself is an exception in phenomena more crucial to something as vast as "the universe", which is mentioned in one of the phrasings of the second law of TD
Important PS:
I am not into Physics (in fact i rather detest Physics, i like Math though), and so i don't know about Brennan's post either, but naturally i would not be able to name any specific phenomenon (even just in the realm of theory) as an example to a possible need for future changes to the second law of thermodynamics
It is useful, though, to note that Entropy was coined as a term to signify the inherent power of the "turning" in the ability of a system to provide energy (work, ergon), much like "energy" means the work/ergon in something's state (eg dynamic, kinetic etc, to use the basic examples from secondary education hated physics).
